The present invention generally relates to power supplies, and particularly relates to switched mode power supplies.
Numerous mechanisms exist for implementing switched mode power supplies (SMPSs). The use of a switched inductor output circuit stands as a non-limiting example of one common implementation. In switched inductor topologies, the SMPS actively regulates its output voltage by switching the output inductor into and out of electrical connection with a supply voltage according to some form of regulation error feedback signal or other regulation control signal. Active regulation sometimes is referred to as “continuous conduction mode” (CCM) operation, denoting the ongoing high/low switching of the output inductor.
More sophisticated SMPSs improve their overall operating efficiencies by operating in “discontinuous conduction mode” (DCM) under certain load conditions. For example, a given SMPS may be configured to enter DCM responsive to detecting zero or negative load current conditions. In other words, when the load current drawn from the SMPS by its load falls to zero, or becomes negative, the SMPS improves its overall operating efficiency by suspending its active regulation switching operations, i.e., it turns its switched output off and allows the load to “float.”
While DCM improves efficiency, its advantages come at the expense of potential problems. For example, the typical SMPS does not provide a sink for negative load current while operating in DCM, so the load voltage may float to undesirably high levels. High float voltages risk damaging the load or the SMPS. Alternatively, if the SMPS does provide a current sink for negative load current during DCM, the amount of current sunk by the SMPS may rise to undesirably high levels.